1. Field of the Invention
This invention is related to a magnetic disk storage device, and especially to a magnetic disk storage device assembled with an improved magnetic head.
2. Discussion of the Background
In conventional magnetic disk storage devices, the signal recording and reproduction are generally carried out with a single magnetic head for the whole surface of a magnetic disk.
FIG. 20 shows an example of the conventional magnetic disk storage device. In this figure, reference 1 shows a magnetic disk, 2 shows a head slider, and 3 is a gimbal which supports the head slider 2. In conventional devices, a single head gap is generally provided for one head slider 2, and the signal recording and reproduction are carried out for the entire data recording and reproduction area on magnetic disk 1 using this head.
Consequently, one head has to move from the innermost circumference to the outermost circumference of the data recording and reproduction area as shown in FIG. 20. This causes a problem in that it increases the seeking distance of the head. The reference 4 in FIG. 20 indicates the effective area of the disk 1. The time required for seeking by the head is proportionate to a 1/2 multiple of the seek distance assuming that the thrust of the head actuator is fixed. In response to a large demand for high speed and large capacity in this magnetic disk storage device, the seek distance must be shortened to achieve the high speed. An effective reduction of the seek distance is demanded for the purpose. There is a magnetic disk storage device provided with two sets of heads 2 and gimbals 3 on an actuator for the one face of a disk 1 as shown in FIG. 21 for the reduction seek distance 4. In this figure, two head sliders 2 take charge of the data recording and reproducing for the inner half and outer half of the recording and reproduction area, respectively. This reduces the seek distance 4 by a half as compared with the case of a single head.
In fact, however, since twice the number of the head sliders 2 and gimbals 3 are needed for this purpose, the weight of the actuator increases as a whole. On the other hand, since the seek time is proportionate to a 1/2 multiple of the weight of the head actuator, the increase in the weight of the head actuator acts against the purpose of shortening the seek time. Then is is necessary to shorten the seek time without increasing the weight of the head actuator.
In the case where two sets of head sliders 2 and gimbals 3 are used like this, two areas of landing zones 5 are required in a contact start/stop (CSS) as shown in the oblique lined portions in FIG. 22. Since the width of one landing zone 5 is larger than that of the head slider 2, if two areas of landing zones 5 are provided, a rate occupied by the landing zone 5 in the whole recording and reproduction area increases greatly. This inevitably reduces the effective area where the signal can be recorded and reproduced on the surface of magnetic disk 1. It also goes against the purpose of enlarging the capacity of the magentic disk storage device. Then, another necessity arises to increase the number of heads per face of the magnetic disk 1 without increasing the area of the landing zone 5.
In conventional magnetic disk storage devices, the relative speed between an air bearing surface (ABS) section (ski section) of the head slider 2 and the rotating magnetic disk 1 is proportionate to the distance from the center of rotation of the magnetic disk 1 to the ABS section. The floating force generated in the ABS section is relatively increased as the speed raises.
In the conventional magnetic disk storage devices as shown in FIG, 23, the actually used head is only one side head with good characteristic. The other side head (described by oblique line) is not used. Namely, one head covers the whole of the recoding and reproduction area. A pivot 6 of the gimbal 3 which supports the head slider 2 is positioned on a center line of equal distance from the right and left hands 7. The width and structure of the right and left ABS section 8 of the head slider 2 are the same. When the interval between the two ABS sections 8 is made larger compared to the radius of the magnetic disk 1, the difference in the relative speed between two ABS sections 8 becomes larger. This makes the amount of float different between the right and left ABS sections, and also the floating posture of the head slider 2 unstable. This hinders an exact data recording and reproduction. In this figure, reference 1 shows the magnetic disk and 9 shows a suspension.
In order to improve the tracking density in this magnetic disk storage device by raising the accuracy in positioning, servo information to provide the track positioning data is formed beforehand on the magnetic disk. This is to follow up the track oscillation of its data tracking caused by deformation of the disk due to changes in temperature and humidity by applying a closed loop control to the head to make it follow up the data track accurately according to the servo data.
In this data surface servo method in which the servo data is formed beforehand on the same magnetic disk for the positioning of the head, the surface of the magnetic disk 11 is divided in the circumferential direction to keep the servo data written in a part of its servo sector 12 as shown in FIG. 24. The servo pattern which becomes the servo data at this time consists of servo patterns A, B, C and D which detect the track finely and other servo patterns P, Q and R which detect the track coarsely as shown enlarged in the lower part of FIG. 24. Although, the track can be detected with a 16 tracking cycle in this example, it would be necessary to increase the number of servo patterns to detect the track with a longer cycle.
These servo patterns are formed almost throughout the area of the servo sector 12. This poses a problem in that the head, when there is one, has to move from the innermost circumference to the outermost circumference of the recoding area. This causes the seek distance by the head 13 to become longer. The seek time must be shortened to meet the prevailing demand for a higher speed and capacity for the magnetic disk. For the purpose, it is necessary to reduce the seek distance effectively. There is a servo surface servo method which provides an exclusive surface to form the servo data for positioning on one of a plurality of magnetic disks and an exclusive head for the servo data reproduction.
In this servo surface servo method, one head exclusively for the data reproduction and a plural number of data recording and reproducing heads are mounted on a same head actuator through an gimbal. The biggest problem in this methos lies in the fact that even though the thermal expansion coefficient is assumed to be the same in the disk, head, gimabl and head actuator on both the servo surface and data surface, the amount of a metaphysical change might vary due to depression in the temperature distribution according to location. This causes an off-track condition (a thermal off-track). In addition, the off-track might occur after a lapse of time, due to a change after lapse of time of in their mounting sections, etc.
Futhermore, a combined method of the servo surface servo and sector is also proposed as a method, which is free from such a thermal off-track, which can take the servo zone higher. This method, too, has a shortcoming in that the formatting is worsened due to the increase in the servo data area.
In an effort to shorten the seek distance and to reduce the seek time for the realization of a high speed of the magnetic disk storage device so far, it has been tried to shorten the seek distance by providing two sets of head sliders and gimbals for one magnetic disk surface. In this method, however, the weight of the head actuator increases. This goes against the purpose of shortening the seek time. To the worse, the area of the landing zone is doubled on account of two heads provided in this method, this causing another problem to reduce the effective operating area per one disk surface.
When the width of the head slider was made larger relatively as compared with the radius of the disk in a conventional magnetic disk storage device, a difference occurred in the floating force between the inner and outer sides of the head slider. This caused the floating posture of the head slider to become unstable as a hindrance for an accurate data recoding and reproduction.
In the conventional magnetic disk storage device in which one magnetic head is provided for one head slider, the position of the servo head is apart from that of the data head and also they are connected through many different components such as the gimbal and head actuator, etc. As a result, a thermal off-track occurs due to dispersion of the temperature distribution according to location in the servo surface servo method. While, in the sector servo method, although the thermal off-track does not occur, the servo zone could not be taken higher.
In these servo methods, since the servo data is formed in the same area where the data is recorded and reproduced, the formatting efficiency becomes worse as compared with a non-servo positioning method using a stepping motor, etc. When the servo data is formed on the data surface lest the thermal off-track occurrs for instance, the track density raises, but the formatting efficiency lowers and the data format storage capacity does not raise in proportion to the track density. To move the head acutuator at a high speed to shorten the seek time, it becomes necessary to increase servo patterns to raise the track detecting capacity. This might cause trouble in reducing the effective area where the signal can be recorded and reproduced on one of the disks due to an increase in the rate of the servo data occupying the entire recording area.